At present, several types of personal radiation monitors are used for recording exposure to X-rays, γ-rays, β-radiation, and other kinds of ionizing radiation. The most commonly used are ionization detectors, Geiger counters, and thermoluminescent dosimeters (TLDs).
Ionization detectors and Geiger counters can record and display the dose rate (for example, in mrad/hr), as well as the integrated dose (for example, in rads) in real time. Alarm set points can be programmed for each of these types of monitors with respect to either dose rate or integrated dose. Both types can communicate to personal computers for data logging or firmware updates, and both may be relatively expensive.
TLDs enable radiation dose to be determined based on the emission of photons which occurs when the dosimeter is heated. TLDs are relatively inexpensive, but are generally processed (that is, read out) in specially designed “readers” after a period of exposure time, typically after being deployed or worn for a period of time between one and three months. As such, they provide information only on the integrated dose for the period of time in question, and a dose rate averaged across that same period of time. Their disadvantage, of course, is that any radiation exposure is only learned after the fact, that is, no real time readout is available.
Following the events of Sep. 11, 2001, concern about the potential detonation of radiological-dispersal or “dirty” bombs in major metropolitan areas has grown. To counter this perceived threat, many large-scale detectors have been deployed in ports to monitor shipping containers, at airports, and at other points of entry into the country. In addition, many radiation detectors have been installed on top of and inside buildings in major cities, so that radiation exposure levels may be determined at any time.
In the event of a radiological incident with a serious risk of a radiation leak, such as the detonation of a “dirty” bomb or a crisis at a nuclear reactor site, such as that caused by the earthquake and tsunami in Fukushima, Japan in March 2011, first responders will need to know an individual's exposure level quickly, so that effective triage may be established. Radiation monitors within buildings could be used to assess how a radiation plume is spreading, but the critical information needed to treat exposed patients, or to assuage the fears of those presumed to have been exposed, would be a knowledge of the radiation dose to which individual had actually been exposed.